As CCD video sensors with higher and higher degrees of resolution become available, the traditional approach has been to attempt to reduce the time required for reading out the charge in each pixel. This approach would increase the pixel readout rate (sometimes referred to as the pixel rate, the pixel clock rate, or the horizontal clock rate) and make it unnecessary to reduce the frame rate. Reducing the frame rate would have the disadvantage of introducing an undesirable flicker into moving images. Recently, however, CCD video sensors with resolutions of as high as one to four megapixels per frame have been developed and the analog technology needed for increasing the pixel rate sufficiently to avoid any reduction in the frame rate is not yet available, especially in an economically practicable form.
One possible approach to a solution of this problem is to accept a lower frame rate in reading the data from a high resolution CCD sensor into a frame store without raising the pixel rate and then to use a digital computer to avoid flicker in the reconstruction of the image on a high resolution video monitor. In such an arrangement, flicker is avoided because each frame is displayed and its image refreshed until the next frame is ready for display. A solution of this nature tends, unfortunately, to be economically impracticable not only because of the high cost of a suitable frame store, which is digital, but also because of the high cost of a digital computer. In addition, both the digital frame store and the computer tend to be bulky, a factor detracting significantly from ready portability.
Another approach to a solution uses multiple (e.g., two) outputs from a high resolution CCD video sensor. Without raising the pixel rate, such a solution reads alternate lines from each frame simultaneously into separate frame stores to create two partial images each of which has only half the lines of the original frame and has an effective frame rate of only half the desired frame rate. A digital computer is then used to blend the two partial images into a single image at the desired frame rate prior to application to a single input high resolution video monitor. This solution, like the one described previously, tends to be economically impracticable because of the high costs of both the frame store and the digital computer and to be undesirably bulky.
It is desirable, therefore, to find an economically feasible and physically compact way to read out the charge in all pixels per frame in a high resolution CCD video sensor without either increasing the pixel rate or decreasing the frame rate in the final display and without using expensive frame stores and digital computers.